Method of electroplating



April 11, 1957 B. A. SCHWARTZ, JR S METHOD OF ELECTROPLATING OriginalFiled July 28, 1960 3 Sheets-Sheet l Mlm.

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April 11, 1967 B. A. SCHWARTZ, JR 3,313,715

METHOD OF ELECTROPLATING 3 Sheets-Sheet 5 Original Filed July 28, 1960United States Patent Chtice 3,313,715 Patented Apr. 11, 1967 3,313,715MEI'HD 0F ELECTRGPLATING Benno A. Schwartz, Jr., Cleveland, (Ehio,assigner to The Steel Improvement and Forge Company, Cleveland, Ohio, acorporation of Ohio Original application July 28, 1960, Ser. No. 45,921,now Patent No. 3,183,176, dated May 11, 1965. Divided and thisapplication Mar. 18, 1965, Ser. No. 440,758 8 Claims. (Cl. 2114-36) Thisapplication is a division of my copending application Ser. No. 45,921,filed July 28, 1960, now Patent No. 3,183,176, issued May 1l, 1965.

This invention relates to a method for electrocleaning andelectroplating, and more particularly to a method for automaticallycarrying out electrolytic cleaning and electroplating operations of thetype in which the surface to be plated is subjected to a rubbing orbrushing action as the electrolytic action takes place.

Electrolytic cleaning and plating operations in which an electrodehaving a porous surface that is saturated with electrolyte is rubberover the surface to be cleaned or plated, are well-known and are widelyand successfully used. Difficulties have arisen with such methods inwhich hand tools are employed, however, because of non-uniformity ofresults, the cost of the labor that is involved and the impracticabilityof plating within cylindrical openings or passageways.

A general object of the present invention, therefore, is the provisionof a method whereby electrolytic cleaning and electroplating operationscan be carried out by machine eciently and at low cost. Another objectis the provision of a method particularly adapted to electroclean'mg andelectroplating the interior surface of cylinders, bores, drilledopenings and the like. A further object is the provision of a method forelectrolytic treatment of internal bores and the like which will assuresimultaneous and uniform rubbing of the surface to be treated while theelectrolytic operation is carried out.

Another object is the provision of a method of electroplating wherebydense, high-quality deposits can be obtained at high rates ofdeposition. Another object is the provision of a method and apparatuswhereby a levelling or smoothing effect is obtained during the platingoperation with electrolytes that are not capable of producing thiseffect with conventional procedures. Another object is the provision ofa method of producing highquality, electro-deposited coatings ofchromium and alloys thereof. Further objects and advantages of theinvention will become apparent from the following description of apreferred form thereof, reference being made to the accompanyingdrawings in which:

FIGURE 1 is a somewhat diagrammatic, isometric view illustrating anapparatus embodying a preferred form of my invention;

FIGURE 2 is a front elevational view, partly in section and on anenlarged scale, of a portion of the apparatus shown in FIGURE 1;

FIGURE 3 is an elevational view, with parts broken away, of theelectrode tool utilized in the apparatus, showing it removed from theapparatus;

FIGURE 4 is a bottom view of the tool, taken as indicated by line 4 4 ofFIGURE l;

FIGURES 5 and 6 are horizontal sections taken along lines 5 5 and 6-6 ofFIGURE 3, respectively; and

FIGURE 7 is a horizontal sectional view taken as indicated by line 7-7of FIGURE 3, but showing the tool in the position it takes when it isinserted in a bore to be treated.

Briey, according to a preferred form of the invention, electrolytictreatment of metal surfaces is carried out by making the part to betreated one electrode of the electrolytic system while the otherelectrode is constituted by an electrically conductive tool having aporous dielectric surface that is brought into contact with the surfaceto be treated and supplied with electrolyte while the tool and thesurface are moved rapidly relative to each other, preferably in aplurality of directions. In the case of -bores or other surfaces ofrevolution, the movements preferably consist in rotation about the axisof the surface and simultaneous reciprocation in a direction parallel tothe axis of the surface. By this means all parts of the surface to betreated receive substantially equal treatment, and thus the surface can-be uniformly cleaned and/or electroplated. The rapid rubbing actionmakes possible production of uniform, highquality deposits at high ratesof deposition in electroplating operations and has an unexpected resultin that the plating operation can be carried out so that the depositedcoatings are given a bright, burnished or satiny appearance by theplating operation itself and without requiring boiling or polishing. Thecirculation of the electrolyte insures that fresh electrolyte is alwayspresent at the surface. The result is that the operation can be carriedout rapidly and economically and produces results of uniformly highquality. The method employed mal-:es possible the rapid production ofelectro-deposited coatings that are highly adherent to the underlyingsurface and that are exceptionally hard, dense and smooth.

The apparatus for carrying out the method consists of a hollow,electrically-conductive tool having a porous surface for engaging thework and through which the electrolyte is caused to ow, and means formoving the porous surface rapidly with respect to the surface beingtreated. This means, in the preferred form of the invention disclosedherein, takes the form of a tool mounted in a conventional drill pressmodied slightly to enable it automatically to carry out the desiredfunctions. The drill press provides a simple, economical and reliablemachine for imparting the required motions to the tool. Preferably, thedesired rubbing force is obtained by the action of centrifugal force onparts of the tool. Thus, the tool can be made of extremely simpleconstruction as will appear below. All that is necessary, then, toenable the operation to be carried out is an appropriate source ofelectric power, which may be of conventional construction, and a simplepump and fluid system for circulating the electrolyte through the tool.

Referring to FIGURE 1, the drill press which forms the basis for theapparatus is indicated in general at 16. The press is of conventionalconstruction and typically may comprise a base 11, a pedestal 12 whichsupports a bed plate 13 and a bracket 14. The bracket carries a spindle15 which supports a conventional chuck 16. As appears below, the tool orelectrode indicated in general at 18, is supported by the chuck. Thespindle is rotated at the desired speed by means of a motor 19 whichdrives the spindle through a belt 20 in a conventional manner.

As will appear in greater detail below, electrolyte is pumped from asump or storage tank 22 by a small, motordriven pump 23 through conduits24 to the tool 18. The electrolyte flows outwardly through the porous,dielectric surface of the tool into Contact with the inner surface ofthe bore in the work W and then falls by gravity into the sump 22.

In order to prevent the electrolyte from splattering and to protect thepress from corrosion, the work is preferably surrounded by a shield 26which may be composed of a transparent plastic. A perforated plasticshield 27 (see FIGURE 2) is also interposed between the work and the bed13 of the drill press. The bed of the press also has openings through itand thus the electrolyte can run 3 out f the work through the plasticshield 27 and the bed into the sump 22. Preferably, the electrolyte ispassed through a filter 23 before it is returned to the work.

The electric power supply lto the plating electrode and the work ispreferably conventional and preferably consists of a conventional DC.supply that is connected to the tool by conductor 31, clamp 32 andconductor 33, and to the work by conductor 35 and clamp 36. The powersupply 30 contains the usual controls and meters, so that the voltageand current density can be controlled to produce the desired results.When the apparatus is used for plating, the tool 18 is made the anodeand the work the cathode; when the apparatus is used for electrolyticcleaning, the polarity is ordinarily reversed, the work being made theanode.

In order to impart the preferred reciprocatory motion to the electrodetool 18, the spindle advancing and retracting mechanism of the drillpress :l0 is employed. In a conventional press such as shown herein,this mechanism embodies a rack and pinion or like mechanism which isactuated by a manually operated handle. The modication of the drillpress to suit the purposes of the present invention requires that theconventional handle be removed and a pinion 38 substituted therefor.Pinion 3S is engaged by a rack 39 which is connected to a piston rod 49attached to piston a1 operating in cylinder 42. The cylinder 42 may besupported from pedestal 12 by any convenient bracket 44.

The piston 41 is caused to reciprocate within the cylinder 42 and thusto reciprocate the rack 39 and move the spindle up and down byalternately connecting the opposite ends of the cylinder to a source offluid, such as air, under pressureand to a discharge port. This may becarried out by means of a conventional solenoid-operated four-way orreversing valve 45 which is connected to the opposite ends of thecylinder by means of conduits 46 and 47, and to a compressor 48 or othersource of uid under pressure by conduits 49. The valve may be ofconventional construction and per se forms no part of the presentinvention. The valve is controlled by a solenoid 50. The speed ofreciprocation of the cylinder may be controlled by a ow control orpressure regulating valve 51 interposed in the line leading to thecompressor.

In order to reverse the operation of the piston, a dog 53 is mounted ona bracket 54 carried by the piston rod 49. The dog is adapted to engageVthe actuating plungers of limit switches 55 and 56. The limit switchesare arranged to control the operation of solenoid valve 45 throughconventional electrical circuits 57 and 58. When the dog 53 engages theswitch 55, the connections through the valve 45 are reversed so thatfluid under pressure, which theretofore had been supplied throughconduit 46, is then supplied through conduit 47 whileconduit 46 isconnected to atmosphere. When the piston reaches the other end of thestroke, dog 53 engages switch 56 and again reverses the connections sothat conduit 46 is connected to the pump and conduit 47 to atmospherestarting the motion of the piston 41 over again in its originaldirection.

In order to control the length of the stroke, the limit switches 55 and56 are adjustably mounted in any convenient manner, for example, on amounting plate 59, the switches being clamped to the plate in thedesired positions of adjustment by clamping screws (not shown) extendingthrough the slots 59a and 59b in the mounting plates.

The apparatus described above functions to rotate and reciprocate in thetool 18. The power supply 30 supplies the required electrical energy tothe tool and the work, and the pump 23 and associated parts supply theelectrolyte to the tool.

As shown particularly in FIGURES 3 to 7, the tool 18 is constructed upona tube 60 which is closed at both ends by plugs 61. The tube is clampedin the chuck 16 of the drill press and thus supports the entire tool. In

order to supply electrolyte to the interior of the tool, a stationarycollar 62 is mounted on the tube 60, the collar having a counterboredrecess 63 therein and openings 64 to which the conduits 24 leading fromthe pump 23 are connected. The tube 6@ is provided with perforations 65in the zone within the counterbored portion 63 so that iiuid enteringthe openings 64 can flow into the interior of the tube 69. The conductor33, which is rigid, also is threaded into the collar 62. This serves tohold the collar 62 against rotation and allow it to supply electricpower thereto.

In order to position the collar 62 on the tube 61], rings 66 and 67 arepositioned above and below the collar 62 on the tube. These make pressfits on the tube which are suficient to prevent substantial leakage ofelectrolyte along the tube since the pressure of the electrolyte isrelatively low; the rings are held in place by means of set screws.Leakage between the rings 66 and 67, which rotate with the tube 60, andthe stationary collars 62 is prevented by rubber packing members 63 and69.

The work-engaging portions of the tool are supported beneath thestationary collar 62 by means of rings 71 and 72 that are secured to thetube 69 by appropriate set screws. These rings pivotally support arcuatework-engaging vanes 73; the vanes are provided with pivot pins 75 attheir opposite ends which engage within' recesses 76 in the rings 71 and72 as shown particularly in FIG- URE 3.

Since the tool 18 acts as an electrode, the tube 60, collar 62, rings 66and 67, rings 71 and 72, and vanes 73 are all made of conductivematerial. Preferably, all parts of the electrode tool are composed ofmaterials that are inert to the electrolyte. Stainless steel issatisfactory for the conductive parts for many services and is used inthe preferred form of tool illustrated herein. For other services,platinum-activated titanium may be required; in other instances, carbonor graphite may be found to be satisfactory.

In order to provide a porous dielectric surface on the vanes 73 forengagement with the work, the vanes are each covered with a layer ofporous dielectric material 78. The materials may consist of anyappropriate electrolyte-permeable dielectric material that will not beattacked by the electrolyte and that will not contaminate theelectrolyte. Felt is satisfactory, but I prefer to employ a perforatedplastic material consisting of a sheet of nylon about 0.031 inch inthickness, having about 70 perforations per square inch, theperforations being about 3x32 inch in diameter. This material has betterWearing qualities than felt. The material is held in place by arcuateclamping members 79 which are secured to the vanes 73 by means of screwsS6. It is to be noted that the vanes, which act as anodes in platingoperations, are spaced from the surface to be plated by the thickness ofthe dielectric material.

In order to provide for the ow of electrolyte into and through thedielectric surfaces that engage the work, the tube 60 is perforated asshown -at 82 in the zone between the rings 71 and 72, and the vanes 73are provided with passages 83 which permit the electrolyte to flow tothe inner surfaces of the porous dielectric covers 78. If desired,grooves 84 may be provided in the outer faces of the vanes in order todistribute the electrolyte more uniformly. These grooves ordinarily arenot essential, however.

Iu practice, the diameter of the tool with the vanes 73 in the positionshown in FIGURE 7 is only slightly less than the diameter of the bore tobe plated. The tool is inserted -in the bore with the vanes in theposition shown in FIGURE 7; when the tool is rotated in the directionindicated, the vanes each swing outwardly a few degrees under theinfluence of centrifugal lforce and also under the influence of thepressure of the electrolyte in the space within the vanes. Theelectrolyte flows through the passages 83 and is distributed by theporous dielectric covers 78 throughout substantially the entire outerarea of each vane.

The speed of rotation of the tool is such that the speed 'at which thedielectric surfaces rub the work is large as compared to the rubbingspeed ordinarily employed or possible in brush plating with hand tools.For example, in plating a bore having an internal diameter of `an inchand a quarter, I have obtained excellent results by rotating the tool ata speed of 1280 rpm. This gives a rubbing speed of a little over 5,000inches per minute or about 84 inches per second. The rubbing speed of 84inches per second is much greater than the rubbing speed ordinarilyemployed in brush plating operations, which usually is about two orthree inches per second and rarely exceeds inches per second when brushplating with hand tools.

Although I have not been able to measure the pressure exerted by thevaries on the work, calculations indicate that the pressure of the vanesagainst the work is of the order of about three to about five pounds persquare inch at the speeds ordinarily employed. This pressure increasesif the rotational speed of the tool is increased and decreases if therotational speed is decreased.

According to the present invention, the increased rubbing speed isaccompanied by replenishment of electrolyte at the surface to be platedat a much greater rate than is normally employed in brush plating.Conventional brush plating operations are carried out by simply dippinga porous electrode into an electrolyte and then applying it to the work,the electrolyte being replenished every few seconds by redipping thetool in the electrolyte. As distinguished from this, in plating a boreabout 1,2 inches in diameter and about 2 inches long according to thepresent invention, electrolyte is pumped through the tool at the rate ofone-half gallon to one gallon of electrolyte per minute, i.e., about 9to 18 gallons of electrolyte per minute per square foot of surface beingplated. While the electrolyte is circulated in this manner, the tool isrotated at 1280 r.p.rn. as noted above and reciprocated at the rate ofsixty one-quarter inch strokes per minute, the rotation andreciprocation of the tool, coupled with the preferred staggeredarrangement of the perforations in the dielectric integument coveringthe vanes '73, insures the continuous replenishment of the electrolyteover all of the surface being plated at all times during the platingoperation, while the rubbing action physically removes gases andunwanted impurities and other precipitates from the surface to be platedand probably the cathode lm is physically disturbed. The impurities andprecipitates are carried off with the electrolyte that ows out throughthe bottom of the bore and into the sump in the example given and areremoved by filtering the electrolyte. The gases are either carried awaywith the electrolyte or permitted to rise 1nto the atmosphere. In anyevent, it appears that the rubbing at high speed and the rapid rate ofcirculation of electrolyte insures that the electrolyte action takesplace on surfaces that are maintained in clean condition andsubstantially free from gas and with electrolyte that is in goodcondition.

It is also probable that the rapid and alternate wiping of the surfaceto be plated and replenishment of the electrolyte brought about by thetool contributes materially to the success of the present invention. Inthe example given, with about 70 openings per square inch in theinteguments 73, there are slightly more than eight alternate lands orrubbing areas and perforations for each lineal inch of the surface ofthe dielectric material 78. Thus, with the tool rotating at a speed of1280 r.p.m. and the rubbing speed of the dielectric material on the workbeing a little more than 84 inches per second, we find that as the tooltraverses the work the surface of the work is alternately subjected tothe rubbing or wiping `action of the lands and then replenished with theelectrolyte flowing through the perforations at a very high frequency-ofthe order of 650 or more times per second. As each rubbing element orland of the dielectric material passes over the surface, it at leastpartially sweeps away and disturbs the thin film of electrolyte, knownas the cathode film, immediately adjacent the surface and then theelectrolyte is immediately replenished by electrolyte owing through theperforations. The mechanical action of the tool seems to insure theremoval of unwanted products of the electrolysis while the circulationof the electrolyte insures that fresh electrolyte is always available toreplenish the electrolyte that is mechanically swept away. Carrying outthese operations at high speed appears to be one of the factors thatgives unexpectedly advantageous results in the character of filmsdeposited according to my process. The character of the deposit in termsof density and smoothness can also be varied by varying the speed ofrotation of the tool. In general, for a given current density, higherrotational speeds increase the smoothness and density of the deposits,but unexpectedly, by use of high current densities and high rubbingspeeds (which results in increased rubbing pressure) it is possible toproduce deposits that are porous yet smooth as compared to ordinaryporous deposits.

Regardless of the reasons, the results obtained by the use of thepresent invention are unique and remarkably advantageous; and, so far asI am aware, have not been possible of attainment heretofore. Typicalexamples are given below:

Example L A cast iron ibore having an internal diameter Vof about 1.2inches was subjected to the following conventional preliminaryoperations.

(l) Degreasing in a solvent degreasing solution.

(2) Anodic degreasing in a solution of sodium hydroxide.

(3) Anodic etching for five seconds using a solution of hydrochloricacid with a hand brush plating tool at 13 volts.

(4) Flash plating with a conventional nickel brush plating solution toprovide a nickel coating of approximately .000005 inch using aconventional brush plating tool for approximately 10 seconds.

Thereafter, the bore was plated according to the present invention usingthe tool previously described. The tool was rotated at a speed of 1280r.p.m. and reciprocated for a distance of about 1A inch at the rate ofapproximately 60 strokes per minute. The plating was carried out byusing the following conventional copper cyanide electrolyte:

` Grams Copper cyanide 124 Sodium cyanide Sodium hydroxide 6.25

Water to make one liter.

Using a current of 50 amperes at 14 volts, a bore having an area ofabout 7 square inches was plated with copper to a thickness of .001 inchin 50 seconds. The average current density was slightly in excess ofV1,000 amperes per square foot. The deposit was dense, adherent andsmooth and presented a burnished or polished appearance. Even higherrates of deposition with excellent results can be obtained by usingproprietary brush plating electrolytes, the composition of which is notknown to me, although they are, I believe, electrolytes of the generaltype set forth above with special additives to make possible increasedrates of deposition. For example, I have deposited copper under the samecondition except for increased current densities at rates of from .0010to .0015 inch in thirty seconds, using a proprietary copper platingsolution. This rate is much greater than can be attained yby hand brushplating operations with the same electrolyte, just as the rate with theconventional cyanide electrolyte set forth above is much greater thancan be attained in `ordinary bath plating. Also, the character of theplated deposit is superior from the standpoint of density, adherence andsmooth, shiny appearance.

So far as I am aware, any plating solution that is suit-V able for usein a hand brush plating operation may be used with advantageous `andunexpectedly better results according to the present invention.

The method and apparatus of the invention have given especially usefulresults in the production of very hard chromium iron alloy deposits. Anaqueous electrolyte of the following composition was employed:

Ammonium hydroxide [28% -NHiOI-I] ml./l 60 Chromium ammonium sulfate[CT2(SO4)3 (NH4)2SO424H2O] g./1 Ferrous ammonium sulfate [Feso, (NH4)2so,- 6H2oj g./1 13.5 Magnesium sulfate [MgSO4-7H2O] g./l 25.0 Ammoniumsulfate UNI-I4) 2504] g./l 50.0

This bath is disclosed as Example I in the Snavely et al. Patent No.2,693,444, except that in Example I in the patent, the magnesium sulfatecontent of the'bath is 20 grams per liter andthe bath also includes asmall amount of sodium sulte, which was not used in the electrolyteemployed in my tests.

Example 11.-1n one test, the surface of a bore in cast iron, which hadbeen given the same preliminary treatment set forth in Example I above,including a flash of nickel, was subjected to a plating operation at therotational speed and rate of reciprocation given above with acirculation of one-half gallon of the above chromiumiron electrolyte permintue. The bath temperature was 149 F. The current was 80 amperes andthe average current density was 1650 amperes per square foot. Theplating operation was carried out for a period of ten minutes. Thethickness of the plate was .0005 inch indicating a plating rate of .0030inch per hour. The deposit was adherent, uniform light and satiny in thearea which had been subjected to the brushing action of the tool. Inareas of the -bore that were not subjected to the action of the tool,the coating was loose and black.

Example IIL-In another test, the preliminary treat ment, electrolyte,workpiece and speed of rotation and reciprocation of the tool were thesame as in Example II. The bath temperature was 149 F.; the current was50 amperes, giving a current density of 1030 .amperes per square foot;the time of plating was minutes. This produced a plated coating of .0002inch indicating a plating rate of .0012 inch per hour. The deposit againwas adherent, uniform and shiny in the area that was brushed by the tooland porous, dark and dull in the area that was not brushed. In thisexample, as in the case Of Example II, the plating was very hard.

Example IVj-In this test, all the conditions were the same as in ExampleIII, except that the bath temperature was 144 F., the current wasincreased to 90 amperes giving an average current density of 1850amperes per square foot and the plating operation was carried out for veminutes. The thickness of the plating of .0017 inch indicating a platingrate of .020 inch per hour. The deposit was adherent, uniform, light andsatiny in appearance throughout the area acted upon by the tool. Thehardness tested with a Knoop tester and a 10 gram load gave an averageof 1034, which is equivalent to a Rockwell C hardness of 72.3. Thehardness test was made with the indentation parallel to the surface ofthe plating.

Example V.-In another test, the internal surface of an aluminum tube wasrst subjected to an anodic cleaning and etching operation with the useof a hand brush plating tool and a hydrochloric acid electrolyte andthen given a flash of nickel, by a conventional brush plating operationwith a hand tool. The bore was then plated with the apparatus of thepresent invention operating at a speed of 1280 r.p.m., reciprocating ata rate of sixty one-quarter inch strokes per minute and with the abovechromium-iron electrolyte circulated at the rate of onehalf gallon perminute. The bath temperature was 149 F., the current was 50 amperes, thearea plated 5.7 square inches, giving an average current density of 1260amperes per square foot. The time of plating was 30 minutes whichproduced a uniform, adherent, light and mirror-like coating, having athickness of .0011 inch, indicating a plating rate of .0022 inch perhour. Metallographic examination showed the structure to be dense withonly occasional surface to base metal cracks. The average Knoop hardnessof the plating with indentation parallel to surface was 955, equivalentto 69.2 on the Rockwell C scale. The hardness given in tests of ExamplesIV-and V is unexpectedly high, the hardness of the coating ordinarilyobtained by the method disclosed in the said Snavely et al patentordinarily being 600 to 700 Knoop as recited in the patent. The RockwellC hardnesses of 72.3 and 69.2 compare with usual hardnesses of 45 to 55on the Rockwell C scale obtained with the same type electrolyte in aconventional plating bath.

Another unexpected result of the plating operation is a smoothness ofthe nish. As mentioned above, in all of the examples the plated depositspresented remarkably smooth appearances; in some instances, the metal asplated looks as though it had been burnished. Prolometer tests were madeof the aluminum tube plated in Example V. The surface roughness of theplated sample was 10-13 micro inches r.m.s. A similar aluminum tubesubjected to the saine etching procedure that was used in producing thesample of Example V had prior to plating a surface roughness of 35-45micro inches r.m.s. Thus, the surface roughness was greatly reduced bythe plating operation. This result is contrary to expectation.Ordinarily, chromium plating follows closely the underlying surface andthe roughness of the plated surface, as determined by prolilornetertests, corresponds quite closely to the roughness of the surface priorto plating. The theory underlying the production of the unusually smoothsurfaces is not known to me at present. However, it does not appearlikely that the surface of the tool, which is non-abrasive andrelatively soft and which rubs the work rather lightly, could physicallysmooth out the metal once it has `been deposited. Instead, it seems moreprobable that the tool, in some manner not presently known to me butwhich may result from the probable physical disturbance of the cathodefilm by the dielectric elements of the tool, causes theelectrodeposition to take place in such a way that surface roughness isreduced and the desired smoothness and density is obtained. Anothereffect that I have observed is that the eiciency of the platingoperation is improved as compared with conventional methods; that is, agreater weight of metal is deposited per ampere hour with the presentinvention than with conventional procedures employing the sameelectrolyte.

In general, if the rotational speed of the tool is reducedsubstantially, the coated deposits do `not present as shiny or asburnished an appearance as they do with the higher rotational speedgiven in the preferred example. However, for some purposes, suchsurfaces may be desired and may be adequate, and speeds of the order of400 rpm., or about 1200 inches per minute lineal speed is entirelysatisfactory for many purposes. Increased current density may increasethe porosity and decrease the density of the deposits. In general,current density and rate of deposition can be increased whilemaintaining the quality of the deposit if the rubbing speed and rate ofcirculation of the electrolyte are increased. Again, these factors maybe varied in accordance with the character of the deposits required. Theuse of the method and apparatus of the present invention, however, makespossible the rapid production of high-quality coatings and lends itselfparticularly to automatic coating lines and long production runs. Theapparatus may also be utilized for electrolytic cleaning and etching,and in such uses where conventional electrolytes are employed, similaradvantages of uniformity and high speed of surface treatment areattained.

The chromium plating operation, which produces a strong, adherent,highly polished coating that probably is an alloy of about 94% chromiumand about 6% iron, is extremely advantageous not only from thestandpoint of the quality of the plating, but also because the trivalentchromium bath employed does not give off the noxious fumes associatedwith conventional chromium baths. It is thus possible to carry outchrome plating operations without the use of hoods and without requiringthe precautions that are usually required in order to protect theworkers from the health hazard that is present with ordinary chromiumplating baths.

The smoothness and density of the plated deposits is also of greatimportance. By the use of the present invention, bearing metals such aslead-tin alloys or lead-tinindium alloys can `be plated directly inbores or on shafts if desired; aluminum cylinders and other parts aswe-ll as parts composed of other metals, can be provided withwear-resistant platings of great hardness, and corrosionresistantdeposits of excellent appearance can be produced.

It appears probable that increasing the rubbing speed increases thepolishing, leveling or burnishing effect. Also, the higher the rubbingspeed, the higher the current density that can be employed with theproduction of dense, adherent plating that presents a polished orburnished appearance. For a given electrolyte, there probably is aminimum speed below which the leveling, burnishing or polishing actiondoes not take place regardless of the current density employed, `becausethis effect does not appear to be obtainable with hand brush platingtools.

The apparatus disclosed herein is intended particularly for the platingof bores. It will be appreciated that machines of other types may bedevised which can be utilized to carry out the present method in theplating of external surfaces of revolution, fiat surfaces and surfacesof other shapes.

Those skilled in the art will appreciate that various changes andmodications can be made in the invention without departing from thespirit and scope thereof. The essential characteristics are summarizedin the claims.

I claim:

l. The method of electroplating a metal surface which includes the stepsof making the surface the cathode in an electrical circuit, providing ananode, said surface and said anode both being immersed in a platingelectrolyte, said anode being spaced from said surface by a distance ofthe order of one thirty-second of an inch, circulating the electrolytein contact with said surface and said anode at the rate of from 9 to 18gallons of electrolyte per minute per square foot of surface beingplated, subjecting the surface to a mechanical rubbing action by aporous, non-abrasive, dielectric material disposed between the anode andsaid surface during the plating operation and supplying an electrolyteto the surface through said porous, dielectrical material, the rate ofrubbing being of the order of 80 inches per second and the currentdensity being of the order of from 1,000 to 2,000 amperes per squarefoot.

2. A method according to claim 1 wherein the pressure exerted by thedielectric material on the work is in excess of about three and one-halfpounds per square inch.

3. A method according to claim 1 wherein the surface to be plated isiirst degreased, then plated with a flash of nickel and wherein a coppercyanide electrolyte is circulated through said porous, dielectricmaterial.

4. A method according to claim 1 wherein a trivalent 'l0 chromiumelectrolyte is circulated through said porous, dielectric material.

5. A method according to claim 1 wherein the current density is fromabout 1,000 to about 1,700 amperes per square foot.

6. ri`he method of electroplating a metal surface which includes thesteps of making the surface to be treated the cathode in an electricalcircuit, providing an anode, said anode and said surface both being incontact with an electrolyte, spacing said anode from said `surface by adistance of the order of one thirty-second of an inch, continuouslymechanically rubbing the surface in the zone adjacent the anode withspaced elements of dielectric material that is softer than the surfacebeing plated during the plating operation and continuously supplyingelectrolyte to the surface during the plating operation, the rate ofrubbing being at least 20 inches per second, and the current densitybeing of the order of 1,000 to 2,000 amperes per square foot.

7. The method of electroplating the lsurface of metal parts whichincludes the steps of making the surface to be plated the cathode in anelectrical circuit, providing an anode, said cathode and said anode bothbeing immersed in a plating electrolyte, said anode being spaced fromsaid cathode by a distance of the order of one thirty-second of an inch,circulating the electrolyte in contact with said surface and said anodeand subjecting the `surface to be plated to a mechanical rubbing actionby a non-abrasive, dielectric material disposed between the anode andthe cathode during the plating operation, the rate of rubbing being atleast 20 inches per second and the current density being of the order of1,000 to 2,000 amperes per square foot.

8. The method according to claim 7 wherein electrolyte is circulatedbetween the anode and said surface at the rate of from about 9 to 18gallons per minute per square foot of surface being plated.

References Cited by the Examiner OTHER REFERENCES Mazia: BrushElectrolytic Polishing and Electrolytic Lapping, Frankfort ArsenalTechnical Report No. T1839.

HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner.

W. VAN SISE, Assistant Examiner.

1. THE METHOD OF ELECTROPLATING A METAL SURFACE WHICH INCLUDES THE STEPSOF MAKING THE SURFACE THE CATHODE IN AN ELECTRICAL CIRCUIT, PROVIDING ANANODE, SAID SURFACE AND SAID ANODE BOTH BEING IMMERSED IN A PLATINGELECTROLYTE, SAID ANODE BEING SPACED FROM SAID SURFACE BY A DISTANCE OFTHE ORDER OF ONE THIRTY-SECOND OF AN INCH, CIRCULATING THE ELECTROLYTEIN CONTACT WITH SAID SURFACE AND SAID ANODE AT THE RATE OF FROM 9 TO 18GALLONS OF ELECTROLYTE PER MINUTE PER SQUARE FOOT OF SURFACE BEINGPLATED, SUBJECTING THE SURFACE TO A MECHANICAL RUBBING ACTION BY APOROUS NON-ABRASIVE, DIELECTRIC MATERIAL DISPOSED BETWEEN THE ANODE ANDSAID SURFACE DURING THE PLATING OPERATION AND SUPPLYING AN ELECTROLYTETO THE SURFACE THROUGH SAID POROUS, DIELECTRICAL MATEIAL, THE RATE OFRUBBING BEING OF THE ORDER OF 80 INCHES PER SECOND AND THE CURRENTDENSITY BEING OF THE ORDER OF FROM 1,000 TO 2,000 AMPERES PER SQUAREFOOT.